We previously described a non-invasive method for measurement of pulmonary transvascular protein flux (17,18). That method allows us to determine the mass of a diffusible tracer protein in the pulmonary extravascular space at any time after intravenous tracer administration, and the time to half-equilibration of tracer in the pulmonary extravascular space. Recently, analysis has shown that from this data we can calculate the interstitial volume of distribution of tracer protein in lung (VIS), pulmonary transvascular water flux, and predict the steady-state interstitium/plasma concentration ratio of tracer protein (a function of pulmonary microvascular pressure when lung vascular permeability is normal). We will correlate direct and non-invasive measurements of these 3 parameters (VIS, pulmonary transvascular water flux, and L/P) in sheep with chronic lung lymph fistulas. Animals will be studied under baseline conditions and after a variety of injuries known to cause pulmonary edema. External Radioflux Detection represents a new approach to measurement of extravascular lung water which may be clinically useful. The method is neither flow nor ventilation limited, and has already been shown to be clinically useful in assessment of pulmonary endothelial integrity.